trydeferred.js

/* this is an attempt to use the new then and when functions in Dojo 1.5 to handle a chain of async
actions. The scenario is open 2 databases, get a record from the 2nd db, write a record to the 1st that uses data from that record. save it. This is 4 async steps.
*/

// dfetch is a hack to get a database fetch method wrapped up as a deferred. We could add a
// method to the db class to make this a bit prettier
function dfetch(db, query) {
    var def = new dojo.Deferred();
    db.fetch({
        query: query,
        onComplete: function(items) {
            def.callback(items);
        }
    });
    return def;
}

// likewise dsave is a deferred version of the save method
function dsave(db) {
    var def = new dojo.Deferred();
    db.save({
        onComplete: def.callback,
        onError: def.errback
    });
    return def;
}

// here is the code for the 4 steps
var main = function() {
    var db1, db2;
    // step 1: get the 1st db
    uow.getDatabase({database: 'BigWords', collection: 'gbTry'}).then(function(db) {
        db1 = db;
        // step 2: get the 2nd db
        return uow.getDatabase({database: 'BigWords', collection: 'AlphabetSoupLessons', mode: 'r'});
    }).then(function(db) {
        db2 = db;
        // setp 3: fetch an item
        return dfetch(db2, {});
    }).then(function(items) {
        console.log('items', items[0]);
        var record = { name: 'set1', value: [ items[0]._id ] };
        db1.newItem(record);
        // setp 4: save the new record
        return dsave(db1);
    }).then(function() {
        console.log('all done');
    });
        
};

dojo.ready(main);